Was looking at getting an iFi SPDIF iPurifier for use from an old Micromega CD transport to the DS.

iFi lists 3 conditions for DAC/ Transport pairings to benefit from their device as follows:

The DAC needs to be of a design that does not feature built-in dedicated Jitter Rejection by means other than ASRC (DAC’s with ASRC will benefit from iPurifier SPDIF).

Any DAC using generic PLL based SPDIF Receiver Chips without a secondary precision PLL will benefit, the more the worse the source is, as these receivers generally have no suppression of source jitter in the audible range.

The source must have appreciable levels of jitter and/or signal degradation. If the source is essentially a “perfect” source with low jitter and good waveform connected with a short (1m or less) and high quality cable, there is not a lot the iPurifier SPDIF can improve.

Another area of improvement is possible in systems where both source and DAC have SPDIF inputs without galvanic isolation. In this case the iPurifier SPDIF will provide this isolation and break ground loops that can raise the system noisefloor.

For the S/PDIF input the grounds on the S/PDIF signal are connected tho the signal is DC isolated. For the XLR inputs the signals are DC isolated but the ground is connected. A isolator that isolates the grounds as well as the signals may indeed help if the system as a whole has a groundloop problem caused in part by the interconnects.

I don’t think you need to worry about jitter as much as isolating the ground of the S/PDIF input. In my experience ground loops are one of the most overlooked causes of sonic degradation in systems. On the other hand there are purely passive ground loop isolators based on a transformer which may be just about as effective as any active device (and no I don’t have any specific suggestions except possibly the expensive (but effective) Jensen Transformer isolation devices.)